Co-owned U.S. Pat. No. 3,416,468 discloses a folding table construction having leg braces 88, 89 that slide along a slotted center support 71 as the legs are extended and retracted. Slidable latches 103 have slanted surfaces which engage the rivets of the braces to hold the rivets within the end portions of the slots when the legs are fully extended.
Other patents disclose tables having folding top portions with braces that slide along slotted guide members and in which spring elements are provided to hold the braces in latched or locked condition when the top sections are in fully-extended horizontal positions. Reference may be made to U.S. Pat. Nos. 2,704,680, 245,926, and 188,414. In each case, the spring exerts a force tending to urge the brace into its seated or locked position so that if the spring is overcome by a force applied to unseat the brace, the hinged top section will be free to swing downwardly into its folded position. The spring therefore performs a holding function in what is essentially a single action latch release mechanism. By applying sufficient force in one direction, each such latching mechanism may be released.
Other types of folding tables are known where the pivots for the tops are located so that such tops tend to be stable when they are horizontally disposed even when the latches are released. To fold such a top into a generally vertical condition for storage (or for use of the top as a backrest), a lifting force is therefore normally required to be applied to the top. In addition, the single-action latch must be released. It has been found, however, that if the stability of the top in its horizontal condition is altered by a substantial downward force applied to one edge of the top, so that such downward force along that edge has a similar effect as a lifting force applied to the opposite edge, and if at the same time the single-action latch is unintentionally (or intentionally) released, the table top will pivot into its vertical position. Providing such a latch with a spring element as disclosed in the aforementioned patents would not eliminate the problem because a force applied to the latch sufficient to overcome the spring would still release the top for automatic folding if the top were loaded unequally as described.
Therefore, an object of this invention is to provide a double-action lock release which insures against unintended pivoting of the top of a table from its horizontal operative position into a generally vertical or collapsed position. This object is achieved by providing such a table with a link member which, in a preferred embodiment of the invention, has a L-shaped guide slot that slidably receives the connecting element of another portion of the table. A stop plate overlies the portion of the guide slot and is movably mounted upon the link member for movement between a first position that obstructs sliding movement of the connecting element along the slot and a second position displaced from the slot to permit such sliding movement of the connecting element. Such movement of the stop member between its first and second positions is transverse to the direction of movement of the connecting element along the slot; hence, to release the table for folding action of the top, a user must apply two forces at generally right angles to each other. Since the possibility that both forces might be applied accidentally are negligible, and since two distinct steps are required to execute release of the double-action lock, a user is well protected against sudden folding of the table that might be occasioned by vibration, accidental bumping of the latch mechanism, or deliberate action by a prankster.
The stop plate is hingedly connected to the link member and is urged by a spring into a position that normally obstructs sliding movement of the connecting element along the guide slot. In such a position, the stop plate, or at least a portion of that plate, extends along a plane that is generally parallel with the slotted link member. The stop plate includes a handle portion or extension that may be gripped by a user to pivot the stop plate away from the link member to allow passage of the connecting element along the length of the slot. The handle portion is arranged so that it may be gripped by a user to perform the dual functions of first pivoting the link member to shift the connecting element out of the short end portion of the L-shaped slot and into alignment with the elongated main portion of that slot and, second, to swing the stop plate out of the path of the connecting element as it slides along the main portion of the slot.
Although the stop plate performs a secondary locking function in the double-acting lock mechanism described, it would perform the only locking function if the short end portion of the slot were omitted. Furthermore, the connector element need not necessarily slide within a slot extending along the guide link; in a second embodiment, the connector element externally engages the elongated link member and its sliding movement along that member is normally restrained by a spring-loaded stop plate pivotally supported in a manner similar to that already described.
Other advantages, objects, and features of the invention will become apparent from the specification and drawings.